Variable phase shifters that change the phase of a signal are employed for example in high frequency communication equipment. Variable phase shifters are also employed to shift the phase of a phased array antenna employed in high frequency communication.
Examples of variable phase shifters include for example those in which variable capacitors are connected in parallel to a coupled transmission line. In such a variable phase shifter, the phase can be varied over a range of 100° or greater by voltage control to change the capacity that is connected to the transmission line, however there is a large change in the amplitude of the phase-shifted signal.
As a method to achieve a variable range of phase from 0° to 360° whilst suppressing changes in amplitude there is a method that employs a quadrature generator and a vector-synthesizer. In this method, quadrature signals I (0°), Q (90°), I′ (180°), and Q′ (270°) are generated by the quadrature generator and combined by the vector-synthesizer.
As another method to achieve a variable range of phase from 0° to 360° whilst suppressing changes in amplitude there is a method that employs a discrete phase shifter that outputs discrete quadrature signals, and a reflection phase shifter that varies the phase of an input signal over a range of 0° to 90°. In such a method a phase divider is employed to output signals of each phase of 0°, 90°, 180°, and 270° to the discrete phase shifter. The variable phase shifter employing the phase divider inputs a signal of one of the phases output from the phase divider to the reflection phase shifter, and the reflection phase shifter changes the phase over a range of 0° to 90°. The variable phase shifter employing the phase divider thereby has a variable range of phase from 0° to 360°.
However, in a quadrature generator and a discrete phase shifter, when signals are generated at each phase of 0°, 90°, 180°, and 270° there is, for example, a balun is needed for outputting signals at 0° and 180°. Moreover, in a quadrature generator and a discrete phase shifter, a 90° hybrid coupler is needed for outputting signals with a phase difference of 0° and 90° for each of the signals output from the balun. The balun and hybrid coupler occupy the majority of device surface area of a variable phase shifter and accordingly impede reducing device surface area.
There is a variable phase shifter that employs two variable amplifier means to suppress changes in amplitude by controlling such that amplitude characteristics of each of the variable amplifier means are correlated with each other. In such a variable phase shifter, signals with a phase difference 90° divided by a power divider means are amplified by the variable amplifier means and then combined by a power combining means, such that the phase of the output signal varies in a range of 0° to 90°.